1. Field of the Invention
This invention relates to warning and controls in relation to filter conditions.
2. Relation To Prior Art
There are warning and control devices in relation to filter conditions but none known that communicate predetermined response to predetermined levels of either positive or negative pressure with a convenient self-powered unit in a manner taught by this invention.
Examples of different but related filter warning and control systems are described in the following patent documents. U.S. Pat. No. 5,388,189, issued to Kung, described an alarm filter in an expert system for communications network that was not pressure-operated as taught by this invention. U.S. Pat. No. 5,325,809, issued to Mulle, Jr. described a hair-drier alarm that whistled with negative-pressure intake air when the filter was clogged with hair or other material and prevented negative-pressure entry of air into the hair drier except through the negative-pressure whistle. U.S. Pat. No. 5,124,957, issued to Owens et al, described a chronological or time-based filter alarm that was not pressure-operated as taught by this invention. U.S. Pat. No. 4,325,824, issued to Mitchell et al, described a canister type of engine-oil filter having a bypass valve that bypassed the filter and rotated a pointer to a warning position in response to clogging of the oil filter. U.S. Pat. No. 4,129,856, issued to Humphries, described an intrusion alarm operated in response to reflection of radiation on still and relatively moving objects in a radiation field, not filter condition in response to pressure across the filter as taught by this invention.
Problems with monitoring filter conditions continue to exist.